1. Field of the Invention
The present invention relates to a liquid crystal display device in which control is made by semiconductor devices that are formed by using a crystalline silicon film. The invention can be applied to MIM, passive matrix, active matrix, and other liquid crystal display devices.
2. Description of the Related Art
In recent years, techniques of forming thin-film transistors (TFTs) on an inexpensive glass substrate have been developed at high speed. This is because of an increased demand for higher-resolution liquid crystal display devices as display media of multimedia.
For example, in an active matrix display device, thin-film transistors are provided for millions of respective pixels arranged in matrix form and charge to enter or exit from each pixel electrode is controlled by the switching function of the thin-film transistor. Image display is performed by controlling the amount of light that passes through a liquid crystal panel by changing the electro-optical characteristic of a liquid crystal in accordance with an image signal supplied from a data line. Since a voltage applied to the liquid crystal is desired to be constant until the next writing, the image signal potential is held by a storage capacitor for a given time.
As a driving method of the above type of liquid crystal display device, the IPS mode now attracts much attention in which a parallel electrode structure is employed and the device is driven by controlling an electric field that is parallel with a substrate.
A liquid crystal display device driven by the IPS mode is featured by a large viewing angle, high contrast, etc. and has thin-film transistors, gate lines, data lines (source lines), pixel electrodes, a common line, and a common electrode extending therefrom in a pixel area on the same substrate.
In particular, in the IPS mode in which a lateral electric field is controlled, each pixel electrode is interposed between common electrodes that are arranged parallel with the pixel electrode so that an electric field applied to the pixel electrode does not influence other pixels etc. Since a certain area should be secured for those electrodes, the open area ratio (aperture ratio), i.e., the ratio of an area which transmits light for display, of the pixel area is lowered.
Further, to secure a sufficient charge holding time, a liquid crystal display requires a structure in which a storage capacitor is added to a pixel electrode. This is not limited to liquid crystal displays driven by the IPS mode, but applicable to conventional liquid crystal display devices.
However, the provision of electrodes for forming storage capacitors (capacitance electrodes) could be a factor of lowering the open area ratio (aperture ratio). In view of this, a technique has been proposed in which capacitance electrodes formed in the same laser as gate lines also serve as a black matrix (U.S. Pat. No. 5,339,181). However, this technique still has a problem that the capacitance electrodes cannot fully serve as the black matrix because of a problem relating to parasitic capacitance.
Another technique has been proposed in which a storage capacitor as mentioned above is formed by utilizing an area where a pixel electrode and a common electrode overlap with each other (Japanese Unexamined Patent Publication No. Hei. 7-36058). However, it is expected that as the degree of electrode miniaturization increases, the area where to form a storage capacitor becomes smaller, making it impossible to secure a necessary and sufficient capacitance. If it is attempted to form a storage capacitor having a necessary capacitance, the area occupied by the capacitance element will necessarily become large, to lower the open area ratio (aperture ratio).
Conventionally, the light quantity of a backlight is increased to compensate for a low open area ratio (low aperture ratio), to thereby secure necessary brightness of a screen, However, because of increased power consumption, this is a large obstacle to incorporation of a liquid crystal display device into devices that are required to be portable.
As described above, a technique is now desired which can secure a necessary storage capacitance without sacrificing the open area ratio (aperture ratio). To improve the open area ratio (aperture ratio) with the IPS mode, it is desired that the electrode width be reduced to less than 1-2 xcexcm. Although submicron or even finer patterning techniques have already been established, they are now encountering difficulties in mass production, resulting in delay of technological progress.
An object of the present invention is, therefore, to propose a technique for forming storage capacitors which well matches fine processing technologies, as well as to provide a technique for forming a pixel area having a large open area ratio (large aperture ratio).
According to one aspect of the invention, there is provided a liquid crystal display device comprising a first substrate comprising a pixel electrode and a common electrode both being made of a conductive material, the common electrode being a black matrix; a second substrate opposed to the first substrate; and a liquid crystal held between the first and second substrates, and driven by an electric field formed between the pixel electrode and the common electrode, the electric field having a component parallel with the substrates.
According to another aspect of the invention, there is provided a liquid crystal display device comprising a first substrate comprising a second interlayer insulating film made of an organic resin material or an inorganic material; a pixel line and a pixel electrode extending from the pixel line which are formed on the second interlayer insulating film; and a third interlayer insulating film and a common electrode, the common electrode being a black matrix; a second substrate opposed to the first substrate; a liquid crystal layer held between the first and second substrates, and driven by an electric field formed between the pixel electrode and the common electrode, the electric field having a component parallel with the substrates; and a storage capacitor formed by at least parts of the pixel line and the black matrix which parts coextend on the second interlayer insulating film with the third interlayer insulating film interposed in between.
According to another aspect of the invention, there is provided a liquid crystal display device comprising a first substrate comprising a second interlayer insulating film made of an organic resin material or an inorganic material; a pixel line and a pixel electrode extending from the pixel line which are formed on the second interlayer insulating film; and a third interlayer insulating film, a common electrode, and a capacitance-forming electrode, the common electrode being a black matrix; a liquid crystal layer held between the first and second substrates, and driven by an electric field formed between the pixel electrode and the common electrode, the electric field having a component parallel with the substrates; and a storage capacitor formed by at least parts of the pixel line and the capacitor-forming electrode which parts coextend on the second interlayer insulating film with the third interlayer insulating film interposed in between.
The invention can be applied to any of the MIM, passive matrix, active matrix, and like liquid crystal display devices. Further, a dispersion-type liquid crystal display device can be constructed by utilizing the invention. In this case, a second substrate is not necessary.
The invention has been made in view of the reduction in the widths of electrodes and wiring lines which will proceed in the future. The techniques of the invention are particularly effective in manufacturing a liquid crystal display device that requires microprocessing.
According to a further aspect of the invention, there is provided a liquid crystal display device comprising an active matrix substrate comprising gate lines and data lines arranged in matrix form on the same active matrix substrate; thin-film transistors formed at respective intersections of the gate lines and the data lines; pixel lines connected to the respective thin-film transistors and pixel electrodes extending from the respective pixel lines; and a common electrode at least partially opposed to each of the pixel electrodes, the common electrode being a black matrix; an opposed substrate that is opposed to the active matrix substrate; and a liquid crystal layer held between the active matrix substrate and the opposed substrate, and driven by an electric field formed between each of the pixel electrodes and the common electrode, the electric field having a component parallel with the substrates.
According to another aspect of the invention, there is provided a liquid crystal display device comprising an active matrix substrate comprising gate lines and data lines arranged in matrix form on the same active matrix substrate; thin-film transistors formed at respective intersections of the gate lines and the data lines; a second interlayer insulating film and a third interlayer insulating film formed above the thin-film transistors; pixel lines connected to the respective thin-film transistors and pixel electrodes extending from the respective pixel lines; and a common electrode at least partially opposed to each of the pixel electrodes, the common electrode being a black matrix; an opposed substrate that is opposed to the active matrix substrate; a liquid crystal layer held between the active matrix substrate and the opposed substrate, and driven by an electric field formed between each of the pixel electrodes and the common electrode, the electric field having a component parallel with the substrates; and storage capacitors each formed by at least parts of the pixel line and the black matrix which parts coextend on the second interlayer insulating film with the third interlayer insulating film interposed in between.
According to another aspect of the invention, there is provided a liquid crystal display device comprising an active matrix substrate comprising gate lines and data lines arranged in matrix form on the same active matrix substrate; thin-film transistors formed at respective intersections of the gate lines and the data lines; a second interlayer insulating film and a third interlayer insulating film formed above the thin-film transistors; pixel lines connected to the respective thin-film transistors and pixel electrodes extending from the respective pixel lines; a common electrode at least partially opposed to each of the pixel electrodes, the common electrode being a black matrix; and capacitor-forming electrodes formed in a layer different than the pixel lines and the pixel electrodes; an opposed substrate that is opposed to the active matrix substrate; a liquid crystal layer held between the active matrix substrate and the opposed substrate, and driven by an electric field formed between each of the pixel electrodes and the common electrode, the electric field having a component parallel with the substrates; and storage capacitors each formed by at least parts of the pixel line and the capacitor-forming electrode which parts coextend on the second interlayer insulating film with the third interlayer insulating film interposed in between.
In the above configurations, the thin-film transistor which controls a voltage applied to the pixel electrode can use, as the active layer, an amorphous silicon film or a crystalline silicon film (polysilicon film).
Where a pixel area is required to have high response speed, where a driver circuit is to be constructed which requires high-speed operation, or in similar cases, it is desirable to employ a thin-film transistor which uses a crystalline silicon film as the active layer.
A thin-film transistor using a crystalline silicon film as the active layer is superior in electrical characteristics to that using an amorphous silicon film. For example, the field-effect mobility is not less than 20 cm2/V.s in the case of an n-channel thin-film transistor and not less than 10 cm2/V.s in the case of a p-channel thin-film transistor.
According to still another aspect of the invention, there is provided a manufacturing method of a liquid crystal display device comprising an active matrix substrate comprising gate lines and data lines arranged in matrix form on the same active matrix substrate; thin-film transistors formed at respective intersections of the gate lines and the data lines, and each having, as an active layer, a crystalline silicon film; a second interlayer insulating film formed above the thin-film transistors; pixel lines connected to the respective thin-film transistors and pixel electrodes extending from the respective pixel lines; and a common electrode at least partially opposed to each of the pixel electrodes; an opposed substrate that is opposed to the active matrix substrate; and a liquid crystal layer held between the active matrix substrate and the opposed substrate, and driven by an electric field formed between each of the pixel electrodes and the common electrode, the electric field having a component parallel with the active matrix substrate, said manufacturing method comprising the steps of forming a second interlayer insulating film made of an organic resin material and/or an inorganic material so as to cover data lines and a first interlayer insulating film that covers gate lines; forming a black matrix on the second interlayer insulating film; forming a third interlayer insulating film so as to cover the black matrix; forming contact holes through the second and third interlayer insulating films; and forming, on the third interlayer insulating film, pixel lines and pixel electrodes extending from the respective pixel lines, wherein each of storage capacitors is formed by at least parts of the pixel line and the black matrix which parts coextend on the second interlayer insulating film with the third interlayer insulating film interposed in between.
According to another aspect of the invention, there is provided a manufacturing method of a liquid crystal display device comprising an active matrix substrate comprising gate lines and data lines arranged in matrix form on the same active matrix substrate; thin-film transistors formed at respective intersections of the gate lines and the data lines, and each having, as an active layer, a crystalline silicon film; a second interlayer insulating film formed above the thin-film transistors; pixel lines connected to the respective thin-film transistors and pixel electrodes extending from the respective pixel lines; and a common electrode at least partially opposed to each of the pixel electrodes; an opposed substrate that is opposed to the active matrix substrate; and a liquid crystal layer held between the active, matrix substrate and the opposed substrate, and driven by an electric field formed between each of the pixel electrodes and the common electrode, the electric field having a component parallel with the active matrix substrate, said manufacturing method comprising the steps of forming a second interlayer insulating film made of an organic resin material and/or an inorganic material so as to cover the data lines and a first interlayer insulating film that covers the gate lines; forming contact holes through the second interlayer insulating film; forming, on the second interlayer insulating film, pixel lines and pixel electrodes extending from the respective pixel lines; forming a third interlayer insulating film so as to cover the pixel lines and the pixel electrodes; and forming a black matrix on the third interlayer insulating film, wherein each of storage capacitors is formed by at least parts of the pixel line and the black matrix which parts coextend on the second interlayer insulating fill with the third interlayer insulating film interposed in between.
One of the main points of the technical means of the invention resides in the commonization of a black matrix and common electrodes. It is intended to realize a configuration in which a lateral electric field is formed between the black matrix (having substantially the same function as the common electrodes) and a pixel electrode that extends from a pixel line.
Further, in a liquid crystal display device having such a parallel electrode structure, a storage capacitor is formed by the black matrix and a pixel line that is connected to a thin-film transistor.
The idea of commonizing the black matrix and the common electrodes, which are considered separate members conventionally, is entirely new, and the formation of the storage capacitor by the black matrix and the pixel line is entirely different from the technique disclosed in the above-mentioned publication No. Hei. 7-36058.
Another important feature of the invention is that a manufacturing process can be simplified greatly by commonizing the black matrix and the common electrodes.
FIGS. 1A and 1B are top views of a pixel region, according to the invention, of a liquid crystal display device. In FIG. 1A, reference numerals 101 and 102 denote a gate line for transmitting a gate signal and a data line for transmitting an image signal, respectively. (In FIG. 1A, the gate lines 101 and the data lines 102 are shown by broken lines because they exist under a black matrix.)
The gate lines 101 and the data lines 102 are arranged in matrix form on the same substrate, and thin-film transistors are disposed for each intersection of those lines. Reference numeral 103 denotes a semiconductor layer that constitutes the active layer of the thin-film transistor. A black matrix 104 (hatched in FIGS. 1A and 1B) are formed above the gate lines 101, the data lines 102, and the semiconductor layer 103 so as to cover those members.
The data lines 102 and the black matrix 104 are insulated from each other by a second interlayer insulating film of 0.1-5.0 xcexcm in thickness. The second interlayer insulating film is made of an organic or inorganic material.
Further, a pixel line 105 and a pixel electrode 106 extending therefrom are formed !above the black matrix 104 through a third interlayer insulating film. FIG. 1B shows a state that the pixel line 105 and the pixel electrode 106 are laid on the structure of FIG. 1A.
Although the pixel line 105 and the pixel electrode 106 constitute an integral part in FIG. 1B, the present inventors clearly distinguish between those members based on their functions. That is, the pixel electrode 106 is defined as the portion extending from the pixel line 105 to the pixel region (i.e., the opening of the black matrix 104).
That is, the pixel line 105 and the pixel electrode 106 are considered entirely different from each other because the pixel line 105 is provided to form a storage capacitor with the black matrix 104 whereas the pixel electrode 106 is provided to form a lateral electric field between itself and the black matrix 104.
In the above structure, a storage capacitor is formed by the black matrix 104 and the pixel line 105 with the third interlayer insulating film interposed in between in the region where the black matrix 104 and the pixel line 105 overlap with each other. The third interlayer insulating film needs to be constituted of an insulating film having a larger relative dielectric constant than the second interlayer insulating film.
Although as shown in FIG. 1B a storage capacitor is formed in the same manner as in the above case in small regions where the pixel electrode 106 exists over the black matrix 104, it can substantially be disregarded in the case of improving the open area ratio (aperture ratio) by reducing the electrode width, which is one of the main points of, the invention.
Lateral electric fields (indicated by arrows in FIG. 1B) for driving the liquid crystal are formed between the pixel electrode 106 and the black matrix 104.